"We were well and truly beaten," Brumbies captain Ben Mowen said.
"The starts to games in the last couple of weeks have been hurting us."
The Bulls made light work of the visitors' brittle defence, constantly bending and breaking it with acute running lines.
Superb veteran lock Victor Matfield was the first to find open space, putting man-of-the-match centre Jan Serfontein over in the eighth minute.
Two penalty goals and then a try to flanker Jono Ross extended the scoreline to 20-3 at the 25th minute.
Having entered half time 23-6, any hopes of a Brumbies comeback were snuffed when first five-eighths Matt Toomua was sent off two minutes after the break for a high tackle.
The Bulls quickly added eight points in his absence, before Brumbies winger Henry Speight crossed for the Brumbies' first try of the match, and his first in 2014.
Skipper Mowen scored after some impressive sideline work by Pat McCabe to reduce the scoreline to 37-18.
However reserve hooker Josh Mann-Rea was sent off in the 74th minute, and the Bulls used their numerical advantage to secure the four-try bonus point through Ross's second try of the match.
Centre Tevita Kuridrani scored a late consolation try, but the Brumbies couldn't find a fourth to earn a bonus point of their own.
The loss puts the Brumbies' 2014 title hopes in a precarious position, as they have only managed to reap one competition point during their fortnight in South Africa.
With the Waratahs jumping to second spot overall after their win over the Rebels, it's the first time the Brumbies haven't led the Australian conference since round four.
-AAP
